Water-based paints are generally composed of aqueous dispersions of polymers and pigments that impart opacity, water resistance, and durability to the dry paint film. The polymers and pigments are dispersed in the liquid paint as discrete particles. Generally, the dispersed polymers comprise the film forming, adhesive portions of the paint. Latex polymers can be prepared by free radical emulsion polymerization processes. Stabilization of the resulting polymer latex particles is achieved by including surfactants in the polymerization reaction. The polymers can also be made from alkyd resins, polyesters and polyurethanes which are preformed in the absence of water, then dispersed in water with the use of surfactants to achieve stable small particle size systems.
The polymer particles in the wet paint tend to form a continuous film by coalescing, i.e., by “melting” or fusing together. The coalescing or film forming process is dependent on various factors, including temperature. In paints, typically, the film forming process of the polymer particles occurs above 25° C. Generally, the temperature at which a polymer undergoes film formation is referred to as its minimum film forming temperature (MFFT). For polymer dispersions, MFFT is the minimum temperature where the various forces which preserve the discrete nature of the polymer particles in a latex (and which are therefore considered barriers to coalescence) are exceeded, resulting in the fusion of the particles. Coalescing solvents are utilized to reduce barriers such as viscous and elastic deformation, facilitating film formation. Effectively, coalescing solvents lower the glass transition temperature (Tg) of the polymer, resulting in a reduction of MFFT such that good film formation can be achieved under more favorable conditions.
2,2,4-trimethyl-1,3-pentanediol monoisobutyrate is known in the art as a coalescing solvent for latex polymers. Once the latex is coalesced/formed into a film, the 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate solvent evaporates off, resulting in the return of the polymer to its original Tg. However, the use of this solvent and others containing volatile organic compounds (VOCs) is becoming discouraged due to health and environmental concerns and government regulation. Other known coalescing ester-based solvents may have low VOC characteristics but do not provide the enhanced wet-scrub resistance, block resistance, gloss and/or dirt pick-up resistance properties that are required for latex-based paints today to meet end use demands.